This invention relates to an electrical precision resistor network comprising two or more electrical resistance elements; it is especially, although not exclusively, applicable to voltage dividers. As used herein "electrical resistance elements" includes an arrangement where one resistance film is split into two or more portions by the interposition between the two ends of the film of one or more terminals for tapping off electricity.
It is often required to produce a network of film electrical resistance elements on a flat insulating substrate such that certain specified electrical parameters of each of said elements will retain a given relationship to those of all other said elements under a variety of different operating conditions including various ambient temperatures and at different levels of power loading. When this requirement is fulfilled, the resulting characteristic is referred to as "tracking" of resistance values; this characteristic is especially important, e.g., in the case of all of the elements in a precision voltage divider network or in so-called ladder networks where a series-connected chain of electrical resistance elements has a voltage applied to its ends and voltage division is achieved by tapping off the required voltage across one or more elements of the chain.
Attempts have been made to achieve satisfactory tracking of the elements by imparting to them substantially the same temperature coefficient of resistance and also arranging for the power loading per unit area of the elements to be constant, but these attempts have not been successful in obtaining precise tracking of the resistance elements.
One of the problems encountered, especially in the production of thin film resistance networks on insulating substrates, is that the surface of the substrate on which the resistance elements are deposited must be very smooth and substrates made from glass have been found useful in this respect. However, it has been found that with networks, e.g. voltage dividers, deposited onto glass substrates the problem of achieving satisfactory tracking of the elements in the network is particularly great.
We have found that in the known arrangement of a network of film electrical resistance elements on a flat insulating substrate, each element and/or parts of single elements if or are at different temperatures and it is this phenomenon which causes the inability to produce satisfactory tracking of resistance values.